Surveillance video is becoming increasingly important, such as for military operations, homeland defense, and law enforcement. For example, the amount of video data produced annually by military unmanned aerial vehicles alone is in the petabyte range, and is growing rapidly. Also, many municipalities and companies use closed-circuit television cameras to monitor activity. For instance, Great Britain alone uses approximately 4.2 million closed circuit cameras throughout its cities (e.g., London). Clearly, efficient analysis of this huge volume of surveillance video requires automatic or interactive techniques.